Spa panel that plugs into existing 240V dryer receptacle--downsides?

[ExMachina]

Live in an old, small house and can't fit another double breaker in the box.

So what I was originally wanting to do is to simply wire a spa panel inline with the existing dryer receptacle.

However, I'm also a cheap bastard and would like to take the spa panel with me when I move. So I'm trying to think of why I shouldn't just attach the spa panel somewhere in between my brew rig and the dryer outlet and simply unplug the dryer / plug in the spa panel when I brew. This should work, right? Anything more I need to consider?

Thanks

 

[doug293cz]

Yes, that will work.

If you need any 120V in your control panel, you really should have a four slot (hot, hot, neutral, ground) dryer receptacle. If you only need 240V in the panel, then a three slot (hot, hot, ground) dryer receptacle is fine.

There is a way to do a three wire to four wire conversion within the spa panel, but it does not comply with the electrical code. The actual risk of using this method is a subject of controversy, and to some extent depends on the lengths of the wiring runs.

Brew on

 

[ExMachina]

Great reply. Of course I would have a 3-prong receptacle

Wonder if it's worth having the receptrical upgraded to a 4-prong? We just had a tree slice through (only) our service neutral about a month ago (fun times!!), and I was reading about how a dropped neutral like that could have suddenly turned our 3-prong dryer into a hazard

 

[augiedoggy]

Great reply. Of course I would have a 3-prong receptacle

Wonder if it's worth having the receptrical upgraded to a 4-prong? We just had a tree slice through (only) our service neutral about a month ago (fun times!!), and I was reading about how a dropped neutral like that could have suddenly turned our 3-prong dryer into a hazard

I believe the 3 prong dryer plug has two hots and a ground no? I thought the nuetral was missing... an appliance with water and 240v and no ground just seems scary to me ungrounded.

 

[ExMachina]

I believe the 3 prong dryer plug has two hots and a ground no? I thought the nuetral was missing... an appliance with water and 240v and no ground just seems scary to me ungrounded.

From what I could find out, the third wire acts as both neutral and ground.

https://diy.stackexchange.com/questions/33602/why-do-240v-circuits-not-require-neutral

So it's safe so long as it all stays connected as it should. But when it fails it may not fail safe.

Looks like I should be able to just replace the breaker, run a 10/4 wire and install a 4 prong outlet...haha..."just"

 

[doug293cz]

From what I could find out, the third wire acts as both neutral and ground.

https://diy.stackexchange.com/questions/33602/why-do-240v-circuits-not-require-neutral

So it's safe so long as it all stays connected as it should. But when it fails it may not fail safe.

Looks like I should be able to just replace the breaker, run a 10/4 wire and install a 4 prong outlet...haha..."just"

Since neutral and ground are bonded together in the main service panel, the third wire in a three wire 240V receptacle can be either neutral or ground. If it is a bare (uninsulated wire) it is intended as a ground only. If insulated it can be considered a neutral or ground. The purpose of a neutral is to carry "return" current in normal operation. The ground is never supposed to carry current in normal operation. Grounds are intended as a safety, and should only carry current in a fault situation. If you use the third wire as a neutral, then you don't really have a safety ground, since the neutral can be at a potential above ground (depending on wire size, run length, and amps conducted.)

You can replace the breaker in the service panel with a GFCI breaker, run 4 conductor wire, and install a 4 slot outlet. Then you will be all set to go. You could also leave the current main panel breaker, run new 4 conductor wire, install a 4 slot receptacle, and use an external spa panel.

Brew on

 

[ExMachina]

Since neutral and ground are bonded together in the main service panel, the third wire in a three wire 240V receptacle can be either neutral or ground. If it is a bare (uninsulated wire) it is intended as a ground only. If insulated it can be considered a neutral or ground. The purpose of a neutral is to carry "return" current in normal operation. The ground is never supposed to carry current in normal operation. Grounds are intended as a safety, and should only carry current in a fault situation. If you use the third wire as a neutral, then you don't really have a safety ground, since the neutral can be at a potential above ground (depending on wire size, run length, and amps conducted.)

You can replace the breaker in the service panel with a GFCI breaker, run 4 conductor wire, and install a 4 slot outlet. Then you will be all set to go. You could also leave the current main panel breaker, run new 4 conductor wire, install a 4 slot receptacle, and use an external spa panel.

Brew on

Yup. Not going to half-ass this. Going to rewire the receptacle (and from what I can see I will need to replace the breaker too)

Many thanks for pointing out this non-obvious detail of the 3- vs 4-prong plug. Saved me some time/frustration I am sure.

 

[brewswithshoes]

Yup. Not going to half-ass this. Going to rewire the receptacle (and from what I can see I will need to replace the breaker too)

Many thanks for pointing out this non-obvious detail of the 3- vs 4-prong plug. Saved me some time/frustration I am sure.

What you are trying to do is exactly how I am wired up now. I move the dryer connection from spa panel into the plug when brewing, and the real dryer's plug back when done. Spa panel ismmounted to wall right next to plug and has its own NEMA pigtail for my setup.

I would check your wire before calling someone out to completely rewire. When I moved into my house my dryer was a 3 prong receptacle and I needed a 4. Thought I was going to have to rewire the whole run, but when I took the receptacle apart I found they had used 4 wire in the run and just clipped back the neutral to where you could barely see it in the wrapped cord. It was a bit of pain to peel it back enough to make an extension off of it to now be 4 wire, but man was it a lot less expensive then a full recable

Still don't know why they used 4 wire and stuck a 3 wire plug receptacle on there. Oh well, worked out for me.

Just saying, you may want to peel the layers back a bit more to see what is there depending on the age of your house. (with the breaker off of course)

 

[ajdelange]

Live in an old, small house and can't fit another double breaker in the box.

Have you looked at the slim style breakers? I've been able to add breakers to completely full older panels by replacing some of the old fat ones in them with the newer slim ones.

We just had a tree slice through (only) our service neutral about a month ago (fun times!!)

Curious as to how your 120V appliances operated (if they did at all) while that line was open.

 

[ajdelange]

There is a way to do a three wire to four wire conversion within the spa panel, but it does not comply with the electrical code.

There is a way to do it which does comply with the code though I've never seen anyone here do it. It requires a transformer with a 140 V primary and a 120 V secondary. The secondary (120VAC) represents a "separately derived system" so that one side can be connected to the ground that comes in with the 240 V feed and at the same time serve as a neutral. Of course you could use a 240:240 V transformer and use the center tap as ground/ neutral but there is no point in doing that as the 240 V loads don't need a neutral and whereas you might want to consider this scheme for a few VA of control circuit load you wouldn't for much more than that as transformers get expensive pretty quickly.

 

[ExMachina]

Have you looked at the slim style breakers? I've been able to add breakers to completely full older panels by replacing some of the old fat ones in them with the newer slim ones.

No. I'll look into that as well. They're not as expensive as I would have guessed!

Curious as to how your 120V appliances operated (if they did at all) while that line was open.

I didn't turn anything on, and the lights did a nice job of "turning" themselves off immediately ("pop" "pop" "pop-pop-pop"). I'd estimate it took us ~10 minutes to figure out that something was very wrong and that it was NOT just a normal power outage. We turned off the main breaker, and waited while the power company fixed it. We were expecting to have lost most of our appliances but miraculously, they were all fine except for the microwave!

What really scared me in retrospect was that this could have easily happened when we were out of the house. Then what? I guess at the very least we'd get to see how long household circuits could manage 240V and what the failure mode would be!

 

[Wizard_of_Frobozz]

If you are going to run new 4-wire and replace the dryer outlet and it's associated breaker, why not consider getting a 30 amp GFCI breaker and install that in the main panel for the dryer circuit?

It's a little more expensive than a spa panel, but you don't have the bulky spa panel taking up space, and you also don't need the extra plugs and receptacle that connect to the spa panel. In the end, I think it's about the same cost.

You can always take the 30 amp breaker with you if you move. You do need to make sure you choose a breaker that is compatible with your panel. The vast majority of homes have Homeline style, so I've been able to reuse mine in 3 different houses now.

https://www.homedepot.com/p/Square-D-Homeline-30-Amp-2-Pole-GFCI-Circuit-Breaker-HOM230GFI/203226674

 

[ajdelange]

I didn't turn anything on, and the lights did a nice job of "turning" themselves off immediately ("pop" "pop" "pop-pop-pop"). I'd estimate it took us ~10 minutes to figure out that something was very wrong and that it was NOT just a normal power outage. We turned off the main breaker, and waited while the power company fixed it. We were expecting to have lost most of our appliances but miraculously, they were all fine except for the microwave!

The loads on the two phases must have been unbalanced. Had they been balanced you would not have noticed anything wrong.

 

[mrstevenund]

I agree with everything said so-far. I have been brewing using a SPA panel since I moved off the kitchen stove. My old house had a 4-wire dryer which I plugged my spa panel into while brewing (also. my chiller water went into the washer ). My current house is new construction and my brewery is in the same room as the breaker panel. I added a dryer outlet just under the panel and still use the same spa panel. 30A breaker in the panel, 50A spa panel used only as a GFI.